LispForum

You have problems, and we're glad to hear them. Explain the problem, what you have tried, and where you got stuck.Feel free to share a little info on yourself and the course.

Forum rules
Please respect your teacher's guidelines. Homework is a learning tool. If we just post answers, we aren't actually helping. When you post questions, be sure to show what you have tried or what you don't understand.

What it's supposed to do is return 0 if the list L is empty or only has one atom (the two base cases) and if not, return 1 plus the depth of the CDR of the list. Whenever I try to test the code, I get an illegal argument error. I tried to test the function with

What it's supposed to do is return 0 if the list L is empty or only has one atom (the two base cases) and if not, return 1 plus the depth of the CDR of the list. Whenever I try to test the code, I get an illegal argument error. I tried to test the function with

Your first problem is the way you call it: (depth (1 2 4)) is attempting to call DEPTH on the result of calling 1 with arguments 2 and 4 -- 1 is not a function, so you get an error. You need to say (depth (quote (1 2 4))) to stop it trying to evaluate (1 2 4) -- or equivalently, (depth '(1 2 4))

The next problem is the structure of your function: a bunch of IFs one after another, but it doesn't return the value they generate -- if L is NIL, the first IF will evaluate to 0, but the code will go on to evaluate the next IF, and then the third, which will evaluate as NIL since the test is false if L is NIL; the function will return NIL, not 0. If the test in the last IF is not NIL, it'll attempt to call 1+ on NIL (since eventually the recursive calls bottom out in the previous case) -- or at least it would if you fixed the syntax there -- but (1+ nil) is an error...

It took a while to see that you're making your own length function. Interestingly, your function has sequential if statements,. Even if NIL was a function (which clearly you mean NULL) The first IF would evaluate to 0 and then it will continue to the second if. You really want to use (if (null L) <then-expression> <else-expression>). The recursion (1+ (depth (cdr L))) lacked parenthesis around depth.

If you have a list '() it should return 0, but if it's '(q) (second L) would return NIL end result is 0 even though the length is clearly 1. I don't think you need more than one base case..